Activation of a cryptic TACTAAC box in the Saccharomyces cerevisiae actin intron.

We constructed a translational fusion between the Saccharomyces cerevisiae actin gene and the Escherichia coli beta-galactosidase structural gene such that expression of beta-galactosidase activity required accurate splicing of the actin intron. Using this chimeric gene, we generated a series of internal deletions which removed the TACTAAC box or, in addition, TACTAAC-like sequences within the intron. Analysis of the fusion transcripts produced in these deletions allowed us to conclude that the TACTAAC-like sequence TACTAAG can substitute, albeit inefficiently, for the authentic TACTAAC box in the splicing process. These results indicate that the yeast splicing machinery can utilize a cryptic TACTAAC box, but there are requirements for primary sequence and proper position.